21 Week Old Baby | Your Baby Week By Week

21 Week Old Baby | Your Baby Week By Week

Your 21 Week Old Baby

You’re probably seeing some big changes in your 21 week old baby during this stage.

She is still in Leap Four, so lots of behind the scenes development is happening in her brain, but you will also observe lots of physical development as well.

Your 21 week old baby is setting up foundations for crawling and sitting in the next few months, meaning lots of workouts on the floor! It’s normal for her to want lots of extra fuel for all this growth, and milk will continue to meet her full needs for a few weeks yet. There’s no need to rush into making solids part of her day. All this growth means disturbed nights are still pretty regular, as she works around the clock to grow towards her next milestones.

Feeding Your 21 Week Old Baby

Although the typical feeding behaviour of babies during developmental stages like Leap Four is being less focused during daytime feeds and more wakeful at night, some babies almost surrender to the demands of their bodies and feed and sleep more during the day. If your 21 week old baby isn’t too distracted by what’s happening around her and most feeds happen in a calm, quiet environment, you could find she drifts easily from feeding into sleep. Unsettled babies who relax when worn in a baby sling or carrier can also go longer periods between feeds, as they sleep away the day and let their body get on with growing.

As long as your 21 week old baby continues to show the reliable signs of getting enough milk, you can be confident she is feeding often enough to meet her needs. It’s natural for her feeding pattern to change as she grows, and she will adapt to the changes in her body as she needs to.

Once you introduce solids, it’s important to continue offering milk before food until around 12 months. Milk – breast or formula – is a compete food source for your baby, and provides all the nutrition and calories they need. As you gradually introduce meat, fruit, vegetables, dairy, grains and other foods into your baby’s diet, they will combine to create a complete diet, but this transition occurs over a period of months. Even in the second year, breastfed babies continue to get a large percentage of their daily intake from breastmilk, while formula fed babies transition to cow’s milk in a cup at around 12 months. Cow’s milk (or substitutes) become part of a toddler’s diet, rather than being the primary food source in the second year. So don’t rush to wean your baby – breast or bottle will continue to be the main part of her diet for many months to come.

Read our article on the 7 most important things you need to know about toddler formula.

Sleep And Settling

There are many reasons why babies feed during the night – hunger and thirst are just two of them. Despite the common sleep myths, the majority of babies do not sleep through the night. Researchers now define this as an 8-hour period of not disturbing their parents, far different from the old scale of just five hours between midnight and 5am, which was used by researchers in the 1950s. In fact, recent studies clearly show 78% of babies aged 6 to 12 months still regularly woke at least once in the night, with 61% having at least one milk feed during the night!

The first year is the most rapid period of growth and development in life. The periods around 4-6 months and 8-10 months are particularly demanding on a baby’s growing body, and increased night waking is typical in these age-groups. It is important to remember your baby is not waking because you haven’t fed her enough during the day. You cannot fill a baby before bedtime in the hope she will sleep longer at night. Extra formula, cereal or rusks in bottles, rice cereal or pureed foods will simply overload your 21 week old baby’s digestive system, and can actually lead to additional wakefulness.

When your baby wakes in the night, a breastfeed will help settle her back to sleep quickly, regardless of why she has woken. Most causes of sleep disturbance in babies cannot be prevented, and sleep training is not considered appropriate in babies under 12 months.

Play And Development

Have you noticed your 21 week old baby working on her core? Tiny baby-crunches are cute to watch, as your baby tries to lift her head while lying on her back. You might even see her lifting her head and legs at the same time! Time to get all those muscles toned as she prepares for crawling. You will also see her tummy time play become more active, as she now takes her upper body weight fully on her outstretched arms. She might even push so hard she slides backwards!

When we celebrate the milestones of mobility, we often overlook the weeks or months of effort babies put in to achieve the strength they need to roll, crawl, sit, stand and walk. The floor is your 21 week old baby’s gym, and she should be spending most of her day freely playing, rather than strapped into seats, strollers or high chairs.

Once she starts moving, she’s going to want to explore her environment, so now is the time to get down on the floor beside her and get a baby’s-eye view of your home. Look for dangling cables, accessible items like games consoles and heavy books and other things she might pull down off low shelves. Spot any sharp corners, trailing blind cords or other low-level dangers which might not be visible from adult height. Even before she crawls, a rolling baby can cover a lot of ground quickly. Bottom-shufflers can move to attractive shelves you thought were out of reach, and the pre-crawler can wriggle and squirm into another room while you think she is immobile! Visit Kidsafe to find out more about making your home safe for your baby.

One reason you are advised to start your baby on solids around six months is the need to boost their iron supply. But why does this happen and should you be worried? Find out more in our article Iron Deficiency And The Exclusively Breastfed Baby.

  • 136


Yvette O'Dowd has been a breastfeeding counsellor and educator since 1992. She has three adult children and a two year old granddaughter - the best sort of bonus baby! Yvette runs a popular natural parenting network, is a babywearing educator, and runs antenatal breastfeeding classes for parents expecting twins and more! She is a keen photographer and scrap-booker and a keeper of a fairy garden.


  1. According to my wonder week app Leap 4 ENDS at 19.5 weeks but your article says a 21 week baby is still in Leap 4. ?

Leave a Reply

Please note: in order to prevent spam and inappropriate language, all comments are moderated before they appear. We appreciate your patience awaiting approval. BellyBelly receives many comments every day, and we are unable to approve them all as soon as they are posted.

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

loaded font roboto